1. Field of the Invention
This invention relates to microwave generating devices and in particular to door seals for use in such devices.
2. Description of the Prior Art
Louis H. Schall, in U.S. Pat. No. 2,956,143, shows a microwave oven wherein the door comprises a flat sheet metal plate to completely close the access opening with marginal overlap contact area for providing an electrical shield against the loss of microwave energy from the oven. In one form, the door seal includes a conductive rubber seal adhesively secured to the wall seat. A series arrangement of seals is provided so that the second seal may dissipate energy leaking past the first seal.
Takeshi Takayama, in U.S. Pat. No. 3,809,843, shows a microwave heating apparatus wherein each of the oven enclosure and the door are provided with complementary stepped structure defining a pair of planes. One of the stepped structures is formed with a cavity having a plurality of walls and a terminating wall. That stepped structure has an opening opposite to the step portion of the other stepped structure. The terminating wall of the cavity is spaced substantially 1/4 wavelength from the middle point intermediate the step portion and the opening and is spaced an integral multiple of 1/2 wavelength from the boundary of the oven interior. A wave absorber is provided comprising rubber material blended with ferrite to absorb any adjacently existing wave without directly blocking the wave path. Thus, the Takayama patent teaches the provision of a door structure which prevents leakage of electromagnetic waves not only in the closed position of the door, but also when the door is slightly spaced from its closed position. The sealing means provides a plurality of seals in sequence along the direction of escape of electromagnetic energy.
John T. Lamb, in U.S. Pat. No. 3,879,595, shows a microwave oven door seal having primary, secondary, and tertiary radiation seals. The primary radiation seal may be capacitive and may be formed between the oven body and the hinged oven door. The secondary radiation seal may be absorbent and may be provided in the door about the access opening. The tertiary radiation seal may be absorbent and mounted in the oven body about the access opening except proximate the hinged edge of the door where the hinge itself is utilized to form the tertiary seal.
A number of other patents disclose a number of similar microwave oven door seals. Illustratively, in U.S. Pat. No. 3,196,242, of Peke J. De Vries et al, a high-frequency oven door seal is disclosed wherein the sealing frame adjoining the feed aperture consists of metal and the following sealing frame consists of a dielectric material in which is distributed a powdered substance which absorbs ultra high-frequency oscillations.
Louis H. Schall, in U.S. Pat. No. 3,196,243, shows a high frequency heating system having a closure door comprising a slotted outer shell enclosing a first removable window means, a second removable window means, and a third perforated metallic window means.
Paul W. Crapuchettes, in U.S. Pat. No. 3,242,303, shows a microwave heating apparatus wherein the boundary of the door overlaps an area of the front wall of the cabinet when the door is in the closed position with the width of this area being equal to a quarter wavelength of the second harmonic frequency of the electromagnetic wave energy supplied to the oven.
George B. Long, in U.S. Pat. No. 3,304,401, shows a microwave oven door closure wherein a shield member includes an imperforate flange overlying a collar on the oven structure defining the opening thereto whereby, when the door is closed, the flange portion of the core will engage the collar to prevent leakage of microwave energy from the interior of the oven around the outer edge of the door closure assembly.
Duane B. Haagensen et al, in U.S. Pat. No. 3,525,841, show a door seal for microwave ovens which includes a first cavity and a second cavity for attenuating and absorbing electromagnetic energy, respectively. Spacers are provided at the four corners of the door to ensure that a proper gap is maintained between the interior surface of the door and corresponding surfaces of the oven housing.
Benjamin V. Valles, in U.S. Pat. No. 3,544,751, shows a microwave oven having meshing microwave door seals. An elongated strip portion formed from and recessed from the oven walls surrounds the oven opening, and the oven door includes an inwardly projecting rim portion which fits within the recess and overlaps substantially the elongated strip portion when the door is in the closed position. A conductive surface of the door overlapping the elongated strip portion with the door closed extends about the inner surface of the oven door spaced inwardly from the rim. This forms a channel between the conductive surface and the rim within which the elongated strip projects when the door is in the closed position. A narrow lining of dielectric is positioned between the conductive surface and the elongated strip, and an attenuative material is positioned between the elongated strip and the rim.
Egbert M. Tingley, in U.S. Pat. No. 3,576,417, shows a construction for electronic oven appliances wherein the escape of microwave energy is prevented by providing inturned flanges for the sidewalls, component tray, and oven floor portions; and the oven door is sealed by means of a compressible annular metallic seal providing a continuous electrical connection between the door and door frame.
In U.S. Pat. No. 3,584,177 of Arnold M. Bucksbaum, an energy seal for microwave oven apparatus is shown as provided along peripheral walls of the door and comprising a short-circuited one-quarter wavelength-type choke structure. The structure is provided with a layer of conductive material adjacent to the wall surfaces to form substantially a double wall and supporting the high leakage currents as a result of the escaping radiated energy to thereby enhance the efficiency of the choke under all operating conditions.
Duane Buford Haagensen, in U.S. Pat. No. 3,629,537, shows a microwave oven door seal having dual cavities fed by a biplanar transmission line. The seal includes a biplanar transmission line which extends in a first direction from within the heating cavity to a point outside the heating cavity. At such point, the biplanar transmission line turns and extends in a second direction away from the access opening. A first electromagnetic wave filter is fed by the first portion of the biplanar transmission line and a second electromagnetic wave filter is fed by the second portion of the biplanar transmission line for reducing the amount of electromagnetic wave energy leaking from the heating cavity. The filters comprise cavities which are located along the biplanar transmission line. The cavities are designed to occupy a minimum of space to provide space for an observation window in the door. Both the width and length of the first portion of the biplanar transmission line on one side of the cavity decrease so that the sealing characteristics thereof remain relatively constant during initial opening movement of the door.
Tetsuo Togashi et al, in U.S. Pat. No. 3,633,564, shows a high-frequency sealing device provided with a hollow metal door having a resilient inner surface for leakageproof contact with the inner edges of the open end of the chamber. Radiation is directed through the hollow interior of the door through an elongated window provided on the inner surface thereof. The door may contain a dielectric for absorption of the leaking wave and its window may be permanently closed with a dielectric, thereby to prevent the entrance of any extraneous matter into the door interior without rendering the window itself impervious to the leaking wave.
In U.S. Pat. No. 3,668,357, Kyozo Kobayashi discloses a microwave seal for electronic range comprising a choke coupling-type microwave cavity communicating with a clearance between a range main body and a door in addition to a microwave seal. The microwave cavity serves to choke the second harmonic frequency component of electrowave energy to prevent the same from leaking from the range while the microwave seal serves to prevent the basic frequency component from leaking.
John M. Osepchuk et al, in U.S. Pat. No. 3,767,884, show an energy seal for high frequency energy apparatus comprising an energy absorbing gasket surrounding the seal to absorb any energy passing outwardly from the energy seal.
In U.S. Pat. No. 3,835,283, Ryuji Suzuki shows a partition and front wall forming choke structure for a microwave oven wherein the seal comprises a first electromagnetic wave labyrinth which is approximately equal in total length to an integral times a half-wavelength of the fundamental wavelength and a second electromagnetic labyrinth which is approximately equal in total length to an odd number of times the quarter-wavelength of the fundamental wavelength.
Michiyo Nakano, in U.S. Pat. No. 3,803,377, shows a microwave oven having combined multiple sealing means. A choke cavity is provided in the door, and a sash is provided on the oven housing which encompasses the door and mounts an absorbing material. An insulating coating separates an inner surface of the aluminum door liner from a corresponding surface of the housing, and a spacing is provided between the door and the surface of the absorbing material adjacent the door.
Bengt Uno Imberg et al, in U.S. Pat. No. 3,985,993, show a sealing arrangement for a microwave oven including a U-shaped door frame defining a quarter-wave choke, first and second seals each comprising an energy absorbent damping material, and a plurality of gaps between the door and the oven's cavity wall and front frame.
Thus, the prior art shows a large number of different types of door seals used in microwave generating devices, such as ovens. The door seals of the prior art are relatively complicated and expensive and have not been found to be fully satisfactory in providing the desirable microwave energy retention for oven devices.